When high-purity argon is used as the refining gas for molten aluminum alloy refining, the argon should be preheated in advance to improve the refining effect. Using preheated argon for refining can produce high temperature and fine and uniform “hot bubbles”, with a small temperature difference with the melt, which is conducive to the stability of the melt refining temperature, avoids the energy consumption of heating, and the dispersion of bubbles. The actual contact area between the refining bubbles and the melt is increased, which is beneficial to bring the gas and inclusions dissolved in the aluminum melt out of the melt surface.
The molten aluminum alloy refining method is: using preheated high-purity argon as a carrier, passing refining flux into 7075 aluminum alloy melt. The Cl2 produced by the decomposition of CCl4 reacts with alkali metals such as hydrogen and sodium and calcium in the melt to generate HCl gas and NaCl, CaCl chloride salts, and the non-metallic inclusions in the melt are accompanied by argon. The bubbles float up to the surface of the melt together.
After refining, while analyzing the chemical composition, the impurities Na and Ca content in the melt are analyzed together. If the Na, and Ca content is relatively high, it needs to be refined again according to the above method. Because Na and Ca not only increase the viscosity of the melt and reduce the casting performance of the alloy, but also make 7075 aluminum alloy “sodium brittle” and increase the cracking tendency of 7075 aluminum alloy round ingots.
Since the Mg element is an alkaline earth metal, there must be a certain amount of Mg element loss during the refining process. When calculating the ingredients, the Mg content is controlled according to the upper limit to compensate for the Mg loss caused by the smelting and refining process. After refining, take samples for analysis and cover the melt with covering flux to prevent the melt from oxidation and hydrogen absorption.